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From: "redbeard0531 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/102876] GCC fails to use constant initialization even when
 it knows the value to initialize
Date: Thu, 21 Oct 2021 13:43:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102876

--- Comment #3 from Mathias Stearn <redbeard0531 at gmail dot com> ---
> Why not just make the function constexpr though?

That isn't always possible. Sometimes the initializer may call a third-party
function that is inline, but not yet marked constexpr (it may need to suppo=
rt
older language versions where it couldn't be constexpr). Other times the
initializer may call a function that is out of line (so can't be constexpr =
at
all), but defined in the same TU. MSVC and clang handle this somewhat more
realistic example nicely, gcc doesn't: https://godbolt.org/z/jYKx8359T

The original example using chrono was just something that when reading I
thought "any optimizer worth its salt should be able to do this even without
explicit constexpr annotation". I was disappointed to learn that gcc couldn=
't,
so I filed a bug in the hope that it can be improved.=